Matthew McNabb, 37, has pleaded not guilty to a charge of aggravated battery of a child during his trial before Judge John Truitt. Prosecutors say McNabb put his then-infant son, Tyler, into a coma resulting in a “permanently vegetative state” on Jan. 1, 2006, by violently shaking him.

Dr. Janice Ophoven testified she could not say what caused Tyler’s coma, but said the boy’s retinal hemorrhaging, brain bleed and swelling of the brain were not enough to diagnose Tyler as a child abuse victim.

“You need evidence of trauma before you can conclude there was abuse,” said Ophoven, a pediatric forensic pathologist based in Minnesota. “You can’t look into a child’s eyes and conclude abuse.”

Defense attorneys Edward Light and Nick Zimmerman attempted to use the testimony to raise doubt in the minds of jurors about the evidence against McNabb.

Ophoven said although it was once accepted by doctors that retinal bleeding and brain damage alone was evidence of shaken baby syndrome, it is now an area of medical science that has fallen into dispute.

Larson’s questions suggested that much of Ophoven’s career consisted of testifying on behalf of child abuse defendants and consulting with defense attorneys. In an emotional case, the questioning became tense.

“It’s dangerous to assume abuse,” Ophoven said.

“It’s also dangerous to ignore evidence that is right in front of you,” Larson shot back.

Truitt was forced to caution the lawyers against getting argumentative as Larson undermined Ophoven’s background and expertise.

Ophoven testified that if Tyler’s condition had been caused by shaking, there would likely have been more evidence such as bruises, fractures or spine trauma. Tyler did not have other obvious signs of child abuse such as broken bones.

Ophoven was allowed to list other possible things that could have caused Tyler’s condition like interrupted Sudden Infant Death Syndrome, choking and others, without actually stating an opinion of what caused his coma.

She argued that if oxygen was cut off to Tyler’s brain by aspirating on his own vomit, it could have caused the bleeding by weakening capillaries in his retinas and brain. Ophoven testified that there was vomit found in Tyler’s lungs, suggesting it might have cut off his air supply.

But Larson pointed out that x-ray reports did not specify vomit was in the baby’s lungs. And she said the baby’s air supply hadn’t been completely shut off, according to statements McNabb gave emergency responders. McNabb said Tyler was gasping for breath in his car seat before he started CPR.

A paramedic who cleared Tyler’s airway as she carried him to the ambulance, said she could tell by the way Tyler’s chest moved that he was getting the air.